Recently, various types of working machines have been automated. For example, various gripping apparatus for gripping and conveying workpieces and parts to predetermined positions have been developed.
The present applicant has disclosed in Laid Open Japanese utility model application laid open No. 58044/1986, apparatus for gripping workpieces and parts, wherein respective gripping pawls are provided in opposition to each other having their rear ends within a housing body. The body defines an air cylinder to which air under pressure, is fed to provide movement for the gripping pawls. Pinions are located in the body which mesh with racks, formed respectively at the ends of the above mentioned gripping pawls, so that the above mentioned gripping pawls may be operated inwardly and outwardly with respect to each other.
However, the above mentioned apparatus is controlled by feeding, exhausting and switching the applied air pressure to the gripping pawls. It is difficult to use to grip fragile glass parts of deformable workpieces and parts. Consequently, such known gripping apparatus has been used only to grip metallic and other workpieces and parts which have comparatively high strength; but it has not been used to grip fragile glass parts or deformable workpieces and parts. In situations involving the gripping of fragile glass parts or deformable workpieces and parts, it is preferable to control the stopping of the gripping pawls, when gripping is completed by detecting the gripping pressure actually applied to the workpieces and parts, or concretely to apply the ideal pressure under which the workpieces and parts are perfectly gripped without being broken or deformed.